1) If you have cheap carpets with loose fibers (check) or pets (check), only clean one room or maybe two at a time. The Roomba's dustbin is limited in size and fills up quickly. As far as I can tell, it has no sensor to tell whether when the dustbin is full. If you limit how much you ask it to clean at one time, then this doesn't become a problem.
2) It is pretty good at getting itself loose if it gets wedged under something, but sometimes it may leave the dustbin behind, like a lizard shedding its tail. It apparently has no sensor to tell that the dustbin has come off, either. If you find it getting wedged under something frequently, I would advise finding a way to move or block off that something before letting the Roomba go. Otherwise you may come back to discover that it has simply been redistributing the dirt instead of collecting it.
3) They are absolutely NOT KIDDING when they advise cleaning the brushes frequently. If you have cheap carpets, pets, or long hair, make that "after every use". Fortunately, doing so is very easy. If you flip it over on its back, the brush and the little rubber-flap-roller are held in by an easily-removed retaining plate. Once you remove the plate, you can take the brush and roller out completely. Both will have carpet fibers, pet hair, and your hair wrapped around them extensively. iRobot supplies a cleaning tool with the Roomba. It resembles a letter opener and makes cutting through the wrapped fibers very easy.
Overall review: using a Roomba is not quite as simple as most of the promotional material would like you to believe — there is more to it than just pushing a button. Depending on your space and furniture, between putting up barriers, taking down barriers, and cleaning the thing, there is some work involved. However, it is still a lot less work than actually vacuuming yourself! It's great for lazy people like me. It's also great for people like my mother, who isn't up to strenuous activity anymore but can still use her hands just fine. The next time I go out to see my parents, I will be taking my Roomba to demo for them.